The Most Impressive Rags-To-Riches Stories Among Today's Top Billionaires

The sums of money possessed by the billionaires atop the Forbes' 400 is so vast and (with some obvious exceptions) their ages so...advanced...that it would seem they had their billions for most of their lives.

And for a substantial number, that is true. The Kochs, Waltons, Marses and Ziffs were all born into families with tremendous wealth.

But the majority acquired their riches using the three G's: gumption, genius and good luck.

And many of them came from nothing.

We have developed an index we thing provides a rough estimate of who has made it the furthest based on where they started. See below for our methodology.

We're calling it the Horatio Alger Index, after the early-20th century author whose fictional tales of rags to riches success stories helped give rise to the notion of "the American dream."

The list is not exhaustive. We worked mostly from the top 50, and for many, we lacked the necessary information, or they declined to provide it.

We gave the most weight to whether one was a first-generation American or a minority, and subtracted the most points if one inherited their wealth.

The greatest determinant was something we called family income proxy value. This is designed to approximate both the wealth (or lack thereof) into which an individual was born, and how developed his neighborhood would have been growing up (and so what resources he or she may have had access to that helped advance their wealth).

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Here's how our formula breaks down:

Family income proxy value: We assigned or deducted five points based on their home area's income positive or negative order of magnitude differential from the national average in the Census year closest to their 16th birthday. For anyone born after 1940, the differential order of magnitude unit is approximately $2,300. So for instance, Jeff Bezos received zero points because Dade, Fla., his home county, had a median family income of $31,238 in 1979; while the national average was $33,374. Meanwhile Howard Schultz' home county of Kings, NY had a median family income of $27,881 in 1969; while the national average was $30,169. County median family income is not available prior to 1959; so for those born prior to 1940 we used state-level per capita personal income data from the BEA. For this group, the order of magnitude differential is $180.